Simplify the following expression: $z = \dfrac{1}{6k} - \dfrac{1}{7k}$
Explanation: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $6k$ and $7k$ $\lcm(6k, 7k) = 42k$ $ z = \dfrac{7}{7} \cdot \dfrac{1}{6k} - \dfrac{6}{6} \cdot \dfrac{1}{7k} $ $z = \dfrac{7}{42k} - \dfrac{6}{42k}$ $z = \dfrac{7 -6}{42k}$ $z = \dfrac{1}{42k}$